1. Technical Field
The present invention relates to a semiconductor optical device and an optical module.
2. Related Arts
For a semiconductor optical device that is designed to be formed on a semiconductor substrate that is made from such as an indium phosphorus or a gallium arsenide or the like, for a semiconductor optical device of a type for receiving and emitting light at an end face in particular, such as an edge-emitting semiconductor laser device or a semiconductor optical amplifier of a waveguide type or a semiconductor photo detector of the waveguide type or the like, a cleaved end face is often made use as an incident facet and an emitting facet at each of such the devices by making use of a cleavability of such the substrate of each of the semiconductors. As typically, a reflection factor at such the end face on the waveguide is determined due to each index of refractions of a semiconductor and an external ambient atmosphere because such the waveguide is designed to be formed in a direction as vertical to the cleaved face. Here, the index of refraction of any semiconductor is assumed to be as approximately three in typical, and then the reflection factor at the cleaved end face is evaluated to be as thirty percent in a case where the external ambient atmosphere is assumed to be as an air that has the index of refraction to be as approximately one. And then therefore it may be available to make use of such the cleaved end face itself for a reflecting mirror. Or, it may be available to make use for a lower reflecting end face or for a higher reflecting end face as well by forming a coating film layer on to such the end face. Moreover, there is provided a method in which a direction of waveguide in a semiconductor optical device is designed to be shifted as intentionally from the direction as vertical to the cleaved end face as a method for reducing the reflection factor at the end face without making use of such the coating film layer, that is disclosed in the following Document 1. And then in accordance with such the method, a cleaved end face 102 is designed to be oblique to a waveguide 101 in a semiconductor optical device 100 that is shown in FIG. 9 (A). And then therefore it becomes possible to reduce an equivalent reflection factor because it becomes difficult for a reflected light to couple again with the waveguide 101 that is reflected at such the cleaved end face (obliquely cleaved end face). Further, there are some cases in which it is desirable to suppress such the reflection factor at the end face as much as possible with depending on a usage of a semiconductor optical device. And then there are a lot of cases in which such a reflection free coating film layer and such the method of the obliquely cleaved end face are made use together. Furthermore, a emitting beam 103 from the waveguide 101 is not designed to be output as vertical to such the cleaved end face 102 but is designed to be output to a direction that is inclined as obliquely thereto in the case where such the obliquely cleaved end face 102 is designed to be made use therefore, that is shown in FIG. 9 (A). And then in a case where the external ambient atmosphere is assumed to be the air, such the emitting beam 103 with having an angle for output to be inclined as approximately three times as an angle of the waveguide 101 against the cleaved end face 102 due to a phenomenon of the refraction that is caused due to the difference on the indexes of refraction of between such the semiconductor and the air.
[Document 1] A. J. Collar et al., “Low residual reflectivity of angled-facet semiconductor laser amplifiers,” IEEE Photonics Technology Letters, volume 2, Issue 8, pp. 553-555, 1990.
In the meantime, however, in a case where the emitting beam 103 from the semiconductor optical device 100 that is disclosed in such as the above mentioned Document 1 is designed to be coupled with such as an optical fiber 104 or another waveguide or the like, that is shown in FIG. 9 (B), it is necessary to devise such as that such the semiconductor optical device 100 is required to be arranged at a sub mount 105 by being inclined to be oblique beforehand or the like. And then it becomes necessary to make use of special bonding equipment in order to perform such the arrangement of the semiconductor optical device 100 on to the sub mount 105 with inclining to be oblique as accurately so as to obtain an angle in accordance with a designing. Or, it becomes necessary to devise on a process of working, such as that a marker for an angle is designed to be introduced into such the sub mount 105 or the like. Moreover, there are some problems of such as that it is difficult to obtain an accuracy regarding a relative positioning of between an emitting facet 101a of the waveguide 101 and an end face on the sub mount 105.
Further, there are other problems in accordance with an array of semiconductor optical devices 110 in which semiconductor optical devices are designed to be arranged in an array form that it is not possible to maintain a gap as uniformly for between each of the semiconductor optical devices in such the array of the semiconductor optical devices 110 and optical part or component because it cannot help but being occurred an interference between the sub mount 105 and the optical part or component (a front part of an array of optical fibers 120 that is shown in FIG. 9 (C)), such as an optical fiber or a waveguide or a lens or the like, due to an occurrence of a shift as gradually with depending on each of such the semiconductor optical devices regarding a positioning of each of emitting facets 110a on the array of the semiconductor optical devices 110 against a line on the sub mount 105, that are shown in FIG. 9 (C). Or, in order to maintain such the gap to be as uniformly, it is excessively difficult to perform a production of an optical module because of such as becoming necessary to make use of special optical part and component, such as an array of optical fibers in which a positioning of each of ends is designed to be shifted gradually or the like.